1. Field
The present invention relates generally to communication systems, and more specifically to variable packet lengths for application to a high rate packet data communications.
2. Background
High Rate Packet Data (HRPD) communications are optimized for bulk data transport. One HRPD system is detailed in the cdma2000, standard referred to as 1xEV-DO and specified in TIA/EIA IS-856 entitled “cdma2000 High Rate Packet Data Air Interface Specification.” FIG. 1 illustrates the air interface layering architecture for a 1xEV-DO system. The Connection layer (CL) provides air link connection establishment and maintenance services. The Security Layer (SL) provides encryption and authentication services. The Physical Layer (PL) provides the channel structure, frequency, power output, modulation and encoding specifications for the Forward and Reverse channels. The Medium Access Control (MAC) layer defines procedures to receive and transmit over the Physical Layer. FIG. 2 illustrates the Forward channel structure, including Pilot, MAC, Control and Traffic channels.
Data is processed as illustrated in FIG. 1, wherein processing of a Connection Layer (CL) packet 102 includes first adding a security layer header 110 and tail 112 to the form a Security Layer (SL) packet 104. The SL packet 104 is then used to generate a Medium Access Control (MAC) layer packet 106, and finally a Physical Layer (PL) packet 108. The MAC layer 106 payload is a fixed number of bits. The PL 108 payload is then a multiple n times the length of the MAC layer 106 payload, plus the length of physical layer overhead (CRC tail bits etc.), wherein n is an integer.
The limitations of the fixed MAC layer 106 payload results in inefficiencies in transmission and thus wasted bandwidth. For example, when the channel condition to a given user is “good” as determined by Signal to Interference and Noise Ratio (SINR) or Data Rate Control (DRC) measure exceeding a threshold, there is a desire to transmit larger packets. For such a user, transmission of smaller blocks of data, such as voice packets, vocoder frames, etc., on the current forward link structure in IS-856 would result in wasted space in the MAC layer 106 packet. As the size of the data is much smaller than the fixed length of the MAC layer 106 packet, the remaining bits are filled with a padding. The result is inefficiency, as the MAC layer 106 packet is not fully utilized.
There is a need, therefore, for a variable packet length for HRD communications, wherein the variable length packets provide efficiency. There is further a need to combine smaller MAC layer 106 packets into a single physical layer packet, allowing data for multiple users to be transmitted per packet.